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Linux: optimize clone3 internal usage

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Add an optimization to avoid calling clone3 when glibc detects that
there is no kernel support.  It also adds __ASSUME_CLONE3, which allows
skipping this optimization and issuing the clone3 syscall directly.

It does not handle the the small window between 5.3 and 5.5 for
posix_spawn (CLONE_CLEAR_SIGHAND was added in 5.5).

Checked on x86_64-linux-gnu.
Reviewed-by: Carlos O'Donell <carlos@redhat.com>
This commit is contained in:
Adhemerval Zanella Netto
2023-01-12 10:58:53 -03:00
committed by Adhemerval Zanella
parent 1e442efd57
commit 98f9435f33
3 changed files with 37 additions and 1 deletions
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5
include/clone_internal.h
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@ -24,6 +24,11 @@ extern int __clone3 (struct clone_args *__cl_args, size_t __size,
fall back to clone or clone2. */ fall back to clone or clone2. */
extern int __clone_internal (struct clone_args *__cl_args, extern int __clone_internal (struct clone_args *__cl_args,
int (*__func) (void *__arg), void *__arg); int (*__func) (void *__arg), void *__arg);
/* clone3 wrapper with a sticky check to avoid re-issuing the syscall if
it fails with ENOSYS. */
extern int __clone3_internal (struct clone_args *cl_args,
int (*func) (void *args), void *arg)
attribute_hidden;
/* The fallback code which calls clone/clone2 based on clone3 arguments. */ /* The fallback code which calls clone/clone2 based on clone3 arguments. */
extern int __clone_internal_fallback (struct clone_args *__cl_args, extern int __clone_internal_fallback (struct clone_args *__cl_args,
int (*__func) (void *__arg), int (*__func) (void *__arg),

24
sysdeps/unix/sysv/linux/clone-internal.c
View File

@ -76,6 +76,28 @@ __clone_internal_fallback (struct clone_args *cl_args,
return ret; return ret;
} }
int
__clone3_internal (struct clone_args *cl_args, int (*func) (void *args),
void *arg)
{
#ifdef HAVE_CLONE3_WRAPPER
# if __ASSUME_CLONE3
return __clone3 (cl_args, sizeof (*cl_args), func, arg);
# else
static int clone3_supported = 1;
if (atomic_load_relaxed (&clone3_supported) == 1)
{
int ret = __clone3 (cl_args, sizeof (*cl_args), func, arg);
if (ret != -1 || errno != ENOSYS)
return ret;
atomic_store_relaxed (&clone3_supported, 0);
}
# endif
#endif
__set_errno (ENOSYS);
return -1;
}
int int
__clone_internal (struct clone_args *cl_args, __clone_internal (struct clone_args *cl_args,
@ -83,7 +105,7 @@ __clone_internal (struct clone_args *cl_args,
{ {
#ifdef HAVE_CLONE3_WRAPPER #ifdef HAVE_CLONE3_WRAPPER
int saved_errno = errno; int saved_errno = errno;
int ret = __clone3 (cl_args, sizeof (*cl_args), func, arg); int ret = __clone3_internal (cl_args, func, arg);
if (ret != -1 || errno != ENOSYS) if (ret != -1 || errno != ENOSYS)
return ret; return ret;

9
sysdeps/unix/sysv/linux/kernel-features.h
View File

@ -241,4 +241,13 @@
# define __ASSUME_FUTEX_LOCK_PI2 0 # define __ASSUME_FUTEX_LOCK_PI2 0
#endif #endif
/* The clone3 system call was introduced across on most architectures in
Linux 5.3. Not all ports implements it, so it should be used along
HAVE_CLONE3_WRAPPER define. */
#if __LINUX_KERNEL_VERSION >= 0x050300
# define __ASSUME_CLONE3 1
#else
# define __ASSUME_CLONE3 0
#endif
#endif /* kernel-features.h */ #endif /* kernel-features.h */